1. Field of the Invention
This invention relates to a process and apparatus for the continuous molding of polymer foam and is more particularly concerned with the production of polymer foam bunstock having a substantially rectangular cross-section.
2. Description of the Prior Art
The production of polymer foam, such as polyurethane, polyisocyanurate, and like rigid foams, in the form of continuous bunstock by depositing foam forming mix in a U-shaped mold comprised of a lower conveyor belt and side panels moving in synchronized manner, is well-known in the art. The bunstock so produced is then generally cut to fabricate sheets, boardstock and the like for insulation purposes. In order to avoid substantial waste of useful foam in the cutting of boardstock and the like from the polymer foam bunstock, it is highly desirable that the bunstock be produced with substantially rectangular cross-section.
A process and apparatus for achieving the above result is described in our issued U.S. Pat. No. 4,128,611. The latter discloses the molding of polymer foam bunstock by depositing polymer foam forming mixture in a conventional moving trough-shaped mold and providing, as the sole shaping means applied to the upper surface of the foam, a panel member pivotally mounted at its downstream end which member floats freely on the foam with its underside in tangential contact with the rising foam in an area immediately following the gel point of the foam but preceding the point at which the foam is no longer sufficiently mobile to be molded without distortion of the cells thereof. The panel member is substantially co-extensive in width with the trough-shaped mold in which the foam is rising. The pressure exerted by the panel member on the foam can be varied in a number of ways; for example by adjusting the angle at which the panel member depends from its pivotal mountings, or by adding or subtracting weights on the upper side of the panel member. In accordance with the usual practice a paper web or like separating sheet is placed on the surface of the rising foam so that the panel member does not make direct contact with the foam.
It has been found that the process and apparatus described in the U.S. Pat. No. 4,128,611 perform in a highly satisfactory manner in respect of the commercial production of most forms of polymer foam bunstock. However, certain polymer foams, particularly those which are based on polyisocyanurate-forming compositions, possess a rise profile which cannot be accommodated readily to the needs of the above process and apparatus. The present invention is devoted to a modification of the process and apparatus of U.S. Pat. No. 4,128,611 which modification serves to meet the needs of polymer foams which are characterized by a particular rise profile which will be discussed in more detail below.
The prior art relating to the preparation of polymer foam bunstock is summarized in detail in the aforesaid U.S. Pat. No. 4,128,611 and will not be repeated here. Since the filing date of the latter patent there has been published British Pat. No. 1,476,177 which describes a process for manufacturing polymer foam bunstock in which the rising foam, during a substantial portion of the rise as well as after the rise is essentially complete, is subjected to continuous pressure from a shaping element which can either be in the form of a single rigid element shaped to follow the contour of the foam rise profile or in the form of two planar rigid members one of which is applied to the foam during its rise and the other after rise is complete. This process and apparatus is clearly distinguished from the process and apparatus to be described below.